(1) Field of the Invention
The present invention relates to a process for preparing aldehydes by hydroformylation of olefins. More particularly, the present invention relates to a process for the preparation of aldehydes by catalytic hydroformylation of olefins with hydrogen and carbon monoxide, in which the reaction is carried out in the presence of a platinum-phosphine complex and a compound of tin and an element of the group VIB of the Periodic Table and aldehydes are prepared in high yields while controlling occurrence of side reactions.
(2) Description of the Prior Art
A hydroformylation catalyst system comprising a platinum-phosphine complex and a tin halide as a promotor has been known. For example, Japanese patent application Laid-Open Specification No. 20112/74 discloses a process in which hydrogen and carbon monoxide are added to an olefin by using a platinum (II) dihalide complex having a improved ligand stabilizing effect in combination with a halide of a metal of the group IVB of the Periodic Table to form a carbonyl group-containing compound. Furthermore, Japanese patent application Laid-Open Specification No. 65810/78 discloses a process for the preparation of aldehydes which comprises reacting an olefin with carbon monoxide and hydrogen in the presence of a catalyst comprising a tetra-valent platinum compound, at least one ligand compound selected from phosphorus compounds represented by the general formula P(R.sup.1, R.sup.2, R.sup.3), amine compounds and tertiary arsine compounds, and a halide of a metal of the group IVB of the Periodic Table. We previously invented processes for the preparation of aldehydes by hydroformylation of olefins using platinum catalysts, in which at least one member selected from halides of metals of the group IVB of the Periodic Table is used as a promotor and a tertiary phosphine of a special steric structure capable of acting as a bidentate ligand is used as the ligand of the platinum catalyst, and filed patent applications for these inventions (see Japanese patent applications No. 26824/78 and No. 5613/79).
In each of these processes, a halide of an element of the group IVB of the Periodic Table, especially a halide of tin, is preferably used as the promotor.
However, when a halide such as stannous chloride is used as the promotor, condensation of a part of the aldehyde formed by the hydroformylation reaction is caused and the yield of the actually obtained aldehyde is drastically reduced by this reaction.
It is considered that one of the causes of this side reaction is that stannous chloride acts as a Lewis acid as is well-known in the art and aldol condensation of the formed aldehyde is caused by the catalytic action of stannous chloride. Occurrence of this side reaction is controlled by reducing the catalyst concentration to a very low level, but in this case, the reaction time is prolonged and the process is not preferred from the practical viewpoint.
We made researches with a view to developing a catalyst capable of guaranteeing a sufficient reaction speed even if the amount used of the catalyst is very small, and found the above-mentioned catalyst system including a bidentate ligand having a special structure which can highly activate a platinum catalyst. However, even if this catalyst system is employed, when the reaction is conducted for a long time, formation of an aldehyde condensate cannot be avoided.
Therefore, we furthered our researches with a view to overcoming the defects of the conventional processes for the preparation of aldehydes, and found that when a compound of tin and an element of the group VIB of the Periodic Table is used instead of a tin halide as the promotor for a platinum catalyst, an aldehyde condensate is hardly formed during or after the reaction even if the catalyst concentration is high. We have now completed the present invention based on this finding.